Effects of rust infection of Senecio vulgaris on competition with lettuce

Paul, Nigel and AYRES, P G (1987) Effects of rust infection of Senecio vulgaris on competition with lettuce. Weed Research, 27 (6). pp. 431-441. ISSN 1365-3180

Abstract

The effects of rust (Puccinia lagenophorae) on competition between groundsel (Senecio vulgaris L.) and lettuce were investigated. In small tubs in a glasshouse environment, rust infection reduced the dry weight yield of groundsel both in monocultures and mixtures with lettuce at total densities from 35 to c. 1100 plants m-2. While rust did not affect the relative mixture response of groundsel it resulted in a significant decrease in the relative mixture response of lettuce. Indeed, the yield-density relationship of lettuce in mixture with rusted groundsel was not significantly different from that of lettuce in monoculture. At 1120 groundsel plants m-2, lettuce yield in mixture with uninoculated groundsel was inhibited by c. 50% when the ratio of lettuce: groundsel (L:G) was 1:3. By contrast, in mixture with rusted groundsel, lettuce yield per tub was not changed by varying L:G, eight lettuce with 24 groundsel yielding no less than 32 in monoculture. Although the severity of rust did not appear to differ, infection inhibited groundsel yield and modified competitive interactions only when L:G was low. In a field experiment the fresh weight yield of lettuce was significantly inhibited by interference from uninoculated groundsel at all sowing densities from 250 to 65 000 seed m-2. Conversely, lettuce yield was not significantly reduced by rust-infected groundsel until weed density exceeded c. 4000 m-2. Even at greater sowing densities, lettuce yield in plots with rusted groundsel was two to three limes greater than in plots with uninoculated groundsel. Inoculation with rust reduced the impact of groundsel upon lettuce yield without causing any significant increase in groundsel mortality. The effects of rust were consistent in both glasshouse and field and were attributed to the decreased competitive ability of infected groundsel plants, especially at high density. The implications of the results for the use of rusts in biocontrol are discussed.